Study On Distribution And Removal Efficiencies Of EDCs In Sewage Treatment Process

One of the available approaches to relieving water resource shortage is utilizing the civil sewage as the persistent and stable water resource. In the secondary effluent, soluble toxic organic micropollutants are one class of uppermost pollutants, which are relatively hard to be biodegradated, and usually consisted of unbiodegradated organics and their intermediateds, as well as the metabolites of microorganism, and most of them are attributed to endocrine disrupting chemicals (EDCs). Therefore, Harbin sewage treatment plants were selected as the investigation targets in the study, the raw sewage, the effluent of each treatment unit, and the active sludge samples in the sewage treatment plants were collected, organic micropollutants in the samples were comprehensively investigated, and correct and reliable sample-pretreating processes and analysis methods were established. The effects of sample-pretreating means, sewage source, sampling seasons and sewage treatment stages on the removal efficiencies of organic micropollutants were examined. The quantification analysis of some prior organic micropollutants with high-toxicity were made. Then alachlor of endocrine disrupting pesticide was chosen as target, and the advanced treatment techniques of photocatalytic oxidation associated with granular active carbon (GAC) adsorption were applying in its degradation, of which operation parameters were designed and the optimum ones were confirmed. The dynamics models of organics removal were established on the basis of experimental data, which supply the design of advanced oxidation technics used in sewage advanced treatment with theoretic basis.In the samples-pretreating processes, the liquid-liquid extraction (LLE)-and solid phase extraction (SPE)-desiccating with anhydrous sodium sulfate methods were separately adopted in the extraction of organic micropollutants in the sewage samples, SPE-silica gel column chromatography-anhydrous sodium sulfate desiccating methods were used in purifying and separating target prior pollutants in sewage, ultrasonic extraction- and soxhlet extraction-silica gel column chromatography-anhydrous sodium sulfate desiccating methods were used in the extraction of organic micropollutants in sludge samples, and the gas chromatogram-mass spectrum (GC-MS) was used in the identification and quantification of them. It was indicated that the calibration curves for quantification of target prior pollutants PCBs, organic nitrogen pesticides (ONPs) and phthalate esters (PAEs) showed excellent linearity in the optimized GC-MS analysis conditions. The evaluation on qualification assurance and qualification control (QA/QC) of analysis methods indicated that the recoveries of targets by SPE-GC-MS method were in the range of 84¹10 percent,and the relative standard deviations were between 1.6 and 8.8 percent, the detection limits were in the range of 0.01 to 0.04 microgramme per liter for PAEs and ONPs, and 0.010 to 0.045 nanogramme per liter.The organic micropollutants confirmed in raw sewage by GC-MS included principally alkyls, alkenes, alcohols, ketones, PAHs, halocarbons, acids, esters, aldehydes, ethers, and nitrousorganics, etc. Thereinto, the proportion of alkyls is larger than others, phthalate esters (PAEs) of EDCs made up of 50 percent or more of esters, organics in the living things and personal care products such as borneol, pharmaceuticals such as cotinine and others were also identified. PAEs were the main priority pollutants in the effluent. The identified organic micropollutants quantity in the influent samples from B sewage treatment plant (BSTP) was greater than that from ASTP by ten species, and total removal efficiencies of organics by BSTP were similarly excellent, but the removal efficiencies in persistent organics were limited. The removal efficiency of organics by the primary sedimentation was unconspicuous, the quantity of organic micropollutants in the effluent of anaerobic active sludge tank got obvious declined, and the total concentration removal efficiencies of organics reached more than 80 percent. The improvement effect of the organics concentration by aerobic active sludge process was unobvious. The quantity of organics in the effluent of secondary treatment was equivalent to that in the effluent of aerobic active sludge tank, but relative total organics concentration fell further. Air floatation unit at the advanced treatment stage made an obvious role in reducing quantity of organics. Both total quantity and total concentrations of organics identified in the O sludge were more than those in the A sludge. The levels of target prior PAEs were higher than those of organic nitrogenous pesticides, and a declined tendence of target analytes'concentration was found with further processing of sewage. The different seasons made great effect on the organics'constitutes in raw sewage, organics identified in December sewage are more than those in May, but the organics constitutions were close, the removal efficiencies by every class of treatment technics were poorer in May.The EDCs pestcide alachlor that was widely applied in agriculture was chosen as representative organic micropollutants in technics experiments. The adsorption effects of simulated alachlor wastewater by GAC in shaking state indicated that the rate equation of alachlor adsorption by GAC accorded to first-order kinetics, and the adsorption process met Freundrich equation very much. In the dynamic state, the conditions of filtrating rate of 1.27 meter per hour, influent temperature of 30 centigrade, and neutral pH were in favor of alachlor adsorption. Both photodegradation rates of alachlor and TOC coincided well with first-order kinetics in fisrt 10 min of the photodegradation reaction, and the kinetics constant value K of alachlor degradation was greater obviously than that of TOC degradation. It was also concluded that prolonging retention time was the key factor in improving the utilization efficiency of H₂O₂ and increasing TOC removal efficiencies. When the retention time was 3 minutes, 100 milligram per liter of H₂O₂ dose, and 25 centigrade of influent temperature were the optimum conditions for TOC removal from the secondary effluent by UV/H₂O₂+GAC systems. The results of alachlor photodegradation mechanism research indicated that more than 20 intermediates came into being, and it was speculated that the final products were acetic acid, propylic acid, carbon dioxide, water, nitric acid, and hydrochloric acid. The GC-MS analysis of organics in the effluent of phtodegradation of the secondary effluent indicated that there were 32 species of organics confirmed, and most of them were nitrogenous organics.